JP2001202914A - Method of observing secondary charged particle image on focused ion beam apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable simultaneous observation of bright and dark areas of a sample caused by the difference in secondary charged particle generation efficiencies by ion beam radiation on a focused ion beam apparatus. SOLUTION: A gain setting for an amplifier 12 in the subsequent stage of a secondary charged particle detector is changed between the bright and the dark area of a sample. A calculation is then performed between signals obtained, to optimize the signals as input signals for an image display apparatus 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating a focused ion beam while scanning a predetermined region of a sample.
The present invention relates to a focused ion beam apparatus for processing a predetermined region of a sample surface and / or observing the sample surface by detecting secondary charged particles generated by focused ion beam irradiation.

In particular, the present invention relates to a method for observing a secondary charged particle image.

[0003]

2. Description of the Related Art Signal processing for an output signal of a secondary charged particle detector will be described with reference to FIG.

As shown in FIG. 1A, secondary charged particles are detected by a detector. The range of the output signal X of the detector is determined by the surface condition of the sample, but does not always match the input signal range of the image display device. Therefore, the arithmetic processing shown in equation (1) is performed by the amplifier so that the detection signal is optimally displayed on the image display device.

Y = A × X + B (1) where X: detector output A: amplifier gain B: amplifier offset Y: image display device input signal At this time, as shown in FIG. When the dynamic range (maximum signal / minimum signal) of the output signal of the image display device is narrower than the dynamic range of the input signal of the image display device, the signal can be optimized by the arithmetic processing shown in Expression (1).

However, depending on the surface condition of the sample, the dynamic range of the output signal of the detector may be wider than the dynamic range of the image display device, as shown in FIG. In such a case, when the arithmetic processing shown in Expression (1) is performed, the result is that the information amount of the output signal of the detector is reduced and output.

Generally, in such a case, a bright region (for example, a region made of a substance having a high secondary electron emission coefficient such as an exposed metal surface) and a dark region (for example, a silicon oxide film) are formed in the observation region. (A region composed of a substance having a small secondary electron emission coefficient). When A and B in Expression (1) are adjusted so that a bright area can be observed, a dark area cannot be observed. Further, if a dark area can be observed, a halation phenomenon in which a bright area shines too brightly occurs, and good observation cannot be performed. On the other hand, if the value of A is set to a small value, sufficient contrast cannot be obtained, which is not practically useful.

Therefore, conventionally, the dynamic range of the storage device is made wider than the dynamic range of the image display device. As an example, the image display device has 128 gradations and the storage device has 1
024 gradations. First, the gain of the amplifier is adjusted so that the signal is not saturated by halation or the like, and the detector signal is stored in the storage device. Thereafter, the stored detector signal is subjected to image processing on an image display device, and a low signal level portion that appears dark is converted to a higher signal level, so that a dark region can be easily observed on the image display device.

[0009]

Since the primary charged particles of the focused ion beam are ions, the difference in the secondary electron emission rate between a bright region and a dark region is about 100 times, and the focused ion beam is different from the case where the primary charged particle is an electron beam. The dynamic range of the output signal of the detector is about 10 times wider.

Therefore, as described above, it is necessary to widen the dynamic range of the storage device, which increases the capacity of the storage device and increases the cost. In addition, the operation of performing signal processing to adjust both the bright area and the dark area so that they can be observed is complicated, and real-time observation cannot be performed.

As a prior art, there is Japanese Patent Application Laid-Open No. 07-073839, but since it is constituted by an analog circuit, a real-time image display cannot be performed because of a signal delay. In addition, since a fast signal passes through an amplifier without being amplified, optimal observation cannot be performed.

Therefore, according to the present invention, in a focused ion beam apparatus, a bright region and a dark region of a sample caused by a difference in generation efficiency of secondary charged particles due to ion beam irradiation can be simultaneously observed in real time with an inexpensive circuit configuration. The task is to do so.

[0013]

In order to solve the above-mentioned problems, the present invention has a configuration as shown in FIG. 2 and changes the gain setting of an amplifier located downstream of a secondary charged particle detector between a bright region and a dark region. Then, an operation is performed between the obtained signals, and the obtained signals are optimized as input signals of the image display device.

That is, an ion source for generating ions,
An electron lens system that converts the ions into a focused ion beam;
A deflection electrode for scanning the focused ion beam, a detector for detecting secondary charged particles emitted from the surface of the sample, an amplifier for amplifying a detection signal of the detector, and a digital signal for the amplified detector signal. A converter for converting, a storage device for storing the two-dimensional intensity distribution, an arithmetic device for calculating the two-dimensional intensity distribution, and displaying a pattern formed on the sample surface based on the intensity distribution of the two-dimensional intensity distribution. A focused ion beam device having a display device adjusts the gain of the first amplifier so that the focused ion beam is scanned and irradiated on the sample surface so that a first observation portion of the sample surface can be observed on the image display device. A first step to determine a first gain and
The second to determine the second gain by adjusting the gain of the second amplifier so as to scan and irradiate the focused ion beam onto the sample surface and adjust the gain of the second amplifier so that the second observation portion of the sample surface can be observed on the image display device Step, the first gain determined in the first step is set in the first amplifier, the focused ion beam is scanned and irradiated on the sample surface, the detection signal of secondary charged particles emitted from the sample surface Amplifying with an amplifier, the third step of storing the obtained two-dimensional intensity distribution in a storage device, and setting the second gain determined in the second step in the second amplifier, and setting the focused ion beam to The detection signal of the secondary charged particles emitted from the sample surface by scanning and irradiating the sample surface was amplified by an amplifier to obtain a two-dimensional intensity distribution, which was stored in a storage device in a fourth step and a third step. Calculate the two-dimensional intensity distribution and the two-dimensional intensity distribution obtained in the fourth step , Providing a fifth step and the observation method of the secondary charged particle image by the focused ion beam apparatus characterized in that it consists of displaying the result to the image display device.

It is not necessary to set the gain in the first step and the second step each time, and the setting once may be used continuously even after the sample is exchanged.

Further, the gain is stored in the first step by converting the signal using a converter having a high resolution and reducing the number of bits of the signal using a data conversion table. By storing the obtained two-dimensional intensity distribution in the storage device and displaying the result on the image display device, the number of components is reduced, and it is not necessary to increase the capacity of the storage device.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Signal processing for an output signal of a secondary charged particle detector will be described with reference to FIG. An ion source that generates ions, an electron lens system that converts the ions into a focused ion beam, and a deflection electrode that scans the focused ion beam focuses the ion beam on the surface of the sample.
It is scanned and illuminated. At this time, secondary charged particles are emitted from the surface of the sample, and the detected intensity is output as an electric signal by the detector. Since this electric signal is weak, it is amplified by the amplifier. The amplified signal is input to the image display device and displayed as a two-dimensional image in synchronization with the scanning signal of the ion beam. The image display device is connected to storage means for storing an image, and a calculation device for calculating the stored image and an input signal.

A configuration example from the amplifier to the image display device will be described with reference to FIG. Output signals of the first and second amplifiers are converted into digital signals by first and second analog / digital converters (A / D) and input to a storage device having a storage capacity of at least one scanning screen. . The storage device is connected to the arithmetic device, and the contents are displayed on the image display device.

A secondary electron image on the sample surface is observed by the following procedure.

(1) The gain of the amplifier is adjusted by scanning and irradiating the focused ion beam onto the sample surface so that a first observation portion of the sample surface, for example, a bright area such as metal, can be observed on the image display device. The gain G1 is determined.

(2) The gain of the amplifier is adjusted by scanning and irradiating the focused ion beam onto the sample surface so that a second observation portion of the sample surface, for example, a silicon oxide film, can be observed on the image display device. To determine.

(3) The gain of the amplifier is set to G1, the focused ion beam is scanned and irradiated on the surface of the sample, and the detection signal of secondary electrons emitted from the surface of the sample is amplified by the amplifier and converted into an analog / digital signal. Are input to the arithmetic unit. In this case, no arithmetic operation is performed, and the arithmetic unit input signal is directly stored in the storage device.

(4) The gain of the amplifier is set to G2, and the focused ion beam is scanned and irradiated on the sample surface to amplify a detection signal of secondary charged particles emitted from the sample surface by the amplifier.
The analog / digital converted signal and the two-dimensional intensity distribution stored in the storage device in (3) are calculated, and the result is displayed on the image display device.

Further, it is not necessary to determine the gain in (1) and (2) each time, and the gain once determined may be used continuously even after the sample is exchanged.

The gain of the amplifier is alternately switched between the first gain and the second gain for each screen scan of the focused ion beam,
The signal may be fetched and calculated with the stored signal, and the result may be stored and displayed. At this time, if the calculation is performed for each pixel, the capacity of the storage device can be saved. In other words, this can be realized with a storage capacity for one screen, and a storage capacity for a plurality of screens is not required.

As for the operation, the input signal and the stored signal may be simply averaged.

If the input signal is expected to saturate, an analog / digital converted signal (digital value)
The signal level can be lowered by adding +1 to the arithmetic unit. For example, if the analog-to-digital converted signal becomes FF and saturates, +1 is added to 00. By performing such a process, the saturated input signal is invalidated. In this case, the operation with the stored signal is an addition. The calculation process in this case is represented by Expression (2).

Y = (G1 × X + 1) + G2 × X (2) where X: detector output G1: gain adjusted in a bright region G2: gain adjusted in a dark region Y: image display device input signal When a signal is repeatedly input, the operation of “calculating the input signal to the arithmetic device and the stored signal, storing and displaying the result” is repeatedly performed.

The process in which the result of the amplification of the detector output by the amplifier in this method is kept within the signal input range of the image display device will be described with reference to FIG. In FIG. 4 (a), the gain is determined so that a relatively low signal level (dark image) of the detector output can be observed by the image display device. In FIG. 4B, the gain is determined so that a relatively high signal level (bright in an image) of the detector output can be observed by the image display device. In both cases, the input to the image display device falls within the input signal range. The results of simple averaging of the image display device input signals in FIGS. 4A and 4B fall within the range of the input signal to the image display device.

Alternatively, an analog / digital converter having a large number of bits is used and its signal is input to a data conversion table. In the data conversion table, different gains are set according to the signal level intensities. By displaying an image with the already obtained two-dimensional intensity distribution, a comparatively low signal level portion of the detector output can be compared. Both high signal level portions can be observed on the image display device.
Further, it is also possible to observe the actually displayed image and change the gain of the data conversion table to make the specific area easier to see. Further, by increasing the number of bits by the analog / digital converter and reducing the number of bits of the signal by the data conversion table, a storage device having a large capacity is not required.

[0031]

As described above, according to the present invention, the gain setting of the amplifier downstream of the secondary charged particle detector is changed between a bright region and a dark region, and an operation is performed between the obtained signals. By optimizing the signal as an image display device input signal, it has been difficult to observe simultaneously with an inexpensive device configuration with a small storage capacity of a storage device. Can be observed at the same time, and by digitally processing the signal,
It can be observed in real time and also prevents fast signals from being displayed on the image without amplification.

Further, a complicated operation such as adjustment of signal processing after capturing an image is not required, and a simple operation for determining the gain of the amplifier in which the observed portion can be observed is sufficient.

Further, by using an analog / digital converter having a large number of bits in combination with a data conversion table, a bright area and a dark area of a sample can be observed simultaneously, and the gain of a specific area can be reduced while observing an image. It has the effect of making it easier to observe by changing it.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example from an amplifier to an image display device.

FIG. 2 is a view for explaining signal processing for an output signal of a secondary charged particle detector.

FIG. 3 is a diagram illustrating signal processing when a data conversion table is used.

FIG. 4 is a diagram illustrating a detector output and an image display device input signal range according to the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsumi Suzuki, Inventor 1-8-8 Nakase, Mihama-ku, Chiba-shi Inside Seiko Instruments Inc. (72) Katsunori Nakazawa 1-8-8 Nakase, Mihama-ku, Chiba-shi Iko Instruments Inc.

Claims (9)

[Claims] A detector for detecting secondary charged particles emitted from a surface of a sample; an amplifier for amplifying a detection signal of the detector; a converter for converting the amplified detector signal into a digital signal; Focusing device having a storage device for storing the two-dimensional intensity distribution, an arithmetic device for calculating the two-dimensional intensity distribution, and a display device for displaying a pattern formed on the sample surface based on the intensity distribution of the two-dimensional intensity distribution Using an ion beam device, two observation parts, a bright area and a dark area on the sample surface,
A method for observing a secondary charged particle image using a focused ion beam device, wherein the image can be simultaneously observed on an image display device. 2. A method for observing a secondary charged particle image by a focused ion beam apparatus according to claim 1, wherein the focused ion beam is scanned and irradiated on a sample surface to display an image of a first observed portion on the sample surface. A first step of determining the first gain by adjusting the gain of the first amplifier so as to be observable by the device; and a second observation of the sample surface by scanning and irradiating the sample surface with the focused ion beam. A second step of adjusting the gain of the second amplifier to determine the second gain so that the portion becomes observable on the image display device; and An amplifier is set, and a detection signal of secondary charged particles emitted from the sample surface by scanning and irradiating the sample surface with the focused ion beam is amplified by the amplifier, and the obtained two-dimensional intensity distribution is stored in a storage device. The third step and the second step determined in the second step The obtained signal is set in a second amplifier, and a detection signal of secondary charged particles emitted from the sample surface by scanning and irradiating the focused ion beam onto the sample surface is amplified by an amplifier to obtain a four-dimensional intensity distribution. And the two-dimensional intensity distribution stored in the storage device in the third step,
A second step of calculating the two-dimensional intensity distribution obtained in the fourth step, and displaying the result on an image display device. Method. 3. A method for observing a secondary charged particle image using the focused ion beam apparatus according to claim 2, wherein the first step, the second step, and the third step are performed without changing the observation place of the sample. And a fourth step and a fifth step, wherein the focused ion beam apparatus observes a secondary charged particle image. 4. A method for observing a secondary charged particle image by a focused ion beam apparatus according to claim 2, wherein the second step is performed after performing the first step and changing a sample or a place where the sample is observed. A method for observing a secondary charged particle image using the focused ion beam device, comprising performing a step, a third step, a fourth step, and a fifth step. 5. A method for observing a secondary charged particle image using the focused ion beam device according to claim 2, wherein the first step and the second step are performed, and a sample or an observation position of the sample is changed. A method for observing a secondary charged particle image using the focused ion beam apparatus, wherein the fourth step and the fifth step are performed later. 6. A method for observing a secondary charged particle image using the focused ion beam device according to claim 1, wherein the focused ion beam is scanned and irradiated on a sample surface to display an image on a first observed portion of the sample surface. The first gain is determined by adjusting the gain of the first amplifier so as to be observable by the apparatus, and the focused ion beam is scanned and irradiated on the sample surface, and the second observation portion of the sample surface is displayed on the image display device. After adjusting the gain of the second amplifier to determine the second gain so that observation is possible, the first gain is set to the first amplifier, and the focused ion beam is scanned and irradiated on the sample surface. The detection signal of the secondary charged particles emitted from the sample surface is amplified by the first amplifier, the obtained two-dimensional intensity distribution and the signal intensity stored in the storage device are calculated, and the result is displayed as an image. Display on the device that the focused ion beam The first step of performing one screen scan of the system, the second gain is set in the amplifier, the detection signal of secondary charged particles emitted from the sample surface by scanning and irradiating the focused ion beam on the sample surface, Amplifying by the second amplifier, calculating the obtained two-dimensional intensity distribution and the signal intensity stored in the storage device, storing the result in the storage device and displaying the result on the image display device, A second charged particle beam observation method using the focused ion beam apparatus, comprising: a second step of performing one screen scan, wherein the first step and the second step are repeatedly performed. 7. A method for observing a secondary charged particle image using the focused ion beam device according to claim 1, wherein the calculation is performed for each pixel of the display device. Observation method of secondary charged particle image by beam device. 8. A detector for detecting secondary charged particles emitted from a surface of a sample, an amplifier for amplifying a detection signal of the detector, a converter for converting the amplified detector signal into a digital signal, A data conversion table for creating a two-dimensional intensity distribution from digital signal data, a storage device for storing the two-dimensional intensity distribution, and a display for displaying a pattern formed on the sample surface based on the intensity distribution of the two-dimensional intensity distribution With the focused ion beam device having the device, two observation portions of a bright region and a dark region of the sample surface are
A method for observing a secondary charged particle image using a focused ion beam device, wherein the image can be simultaneously observed on an image display device. 9. A method for observing a secondary charged particle image using the focused ion beam device according to claim 8, wherein the focused ion beam is scanned and irradiated on the surface of the sample, and the secondary charged particle emitted from the surface of the sample is irradiated with the focused ion beam. The detection signal is amplified by an amplifier, converted into a digital signal using a converter, the two-dimensional intensity distribution obtained using a data conversion table is stored in a storage device, and displayed on an image display device. A method of observing a secondary charged particle image by the focused ion beam device.